The acute effects of hemodialysis on left ventricular (LV) function were studied with the use of externally recorded LV systolic time intervals and echocardiography; 10 patients with normal or near-normal predialysis LV function and no circulatory congestion were studied. Hemodialysis significantly decreased the LV ejection time (LVET) from 270 +/- 9 ms to 237 +/- 10 ms (p less than 0.001); no significant change was noted in the preejection period (PEP). The PEP/LVET ratio increased from 0.41 +/- 0.05 to 0.45 +/- 0.06 (p less than 0.05). The LV end-diastolic dimension decreased from 5.3 +/- 0.3 cm to 4.8 +/- 0.3 cm (p less than 0.001). Fractional shortening and ejection fraction did not change significantly, but hemodialysis slightly increased mean VCF from 1.2 +/- 0.1 s-1 to 1.4 +/- 0.1s-1 (p less than 0.005). Hemodialysis was associated with a 17% decrease (87 +/- 8 ml to 72 +/- 7 ml; p less than 0.001) in LV stroke volume as calculated from echocardiographic data. Small changes in heart rate and blood pressure were insignificant. We conclude that the postdialysis reduction in stroke volume was due primarily to an acute decrease in LV preload; dialysis also appears to be associated with a small increase in the LV contractile state.